This application claims the benefit of Japanese Patent Applications No.2001-056407 filed Mar. 1, 2001, No.2001-073032 filed Mar. 14, 2001, No.2001-073033 filed Mar. 14, 2001, No.2001-073034 filed Mar. 14, 2001, and No.2001-078152 filed Mar. 19, 2001, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to optical deflecting units, optical scanning units, image forming apparatuses and methods of producing optical units, and more particularly to an optical deflecting unit for deflecting a light beam, an optical scanning unit for making a scan using a light beam, an image forming apparatus which uses such an optical scanning unit, and a method of producing an optical unit such as the optical deflecting unit and the optical scanning unit.
2. Description of the Related Art
An optical scanning unit is used in various kinds of apparatuses, including image forming apparatus such as an optical printer, a digital copying machine and a facsimile machine. In order to improve the performance of the optical scanning unit, there are demands to increase the optical scan speed.
One effective way of increasing the optical scan speed is to employ a multi-beam scan method which optically scans a plurality of scanning lines at one time. Regardless of whether a single beam scan method or the multi-beam scan method is employed, it is possible to increase the optical scan speed by increasing the light beam deflection speed.
For example, the light beam deflection speed can be increased by increasing the rotational speed of a rotary polygonal mirror. However, the increased rotational speed of the rotary polygonal mirror inevitably increases the power consumption, vibration and noise, and deteriorates the durability of-the optical deflecting unit itself.
It is also possible to increase the light beam deflection speed by increasing the number of deflection or mirror surfaces of the rotary polygonal mirror, so as to increasing the number of deflections per revolution of the rotary polygonal mirror. However, if the number of deflection or mirror surfaces is simply increased, the radius of the rotary polygonal mirror inevitably increases. Because the inertia of the rotary polygonal mirror is proportional to the square of the radius of the rotary polygonal mirror, the power consumption required to rotate the rotary polygonal mirror having the large radius inevitably increases.
In order to avoid increasing the power consumption, it is necessary to increase the number of deflection or mirror surfaces of the rotary polygonal mirror without increasing the radius of the rotary polygonal mirror. But in this case, the area of each deflection or mirror surface becomes small, to thereby reduce the deflection angle of the light beam. As a result, it becomes necessary to increase the length of the optical path from the rotary polygonal mirror to the scanning surface, so as to obtain the length of the optical scan region that is required for the optical scan. Consequently, the optical scanning unit becomes large.
Other than the rotary polygonal mirror, there is an optical deflecting unit which uses a torsion mirror. This torsion mirror is sometimes also referred to as a torsional scanning mirror or a torsional resonant mirror. The torsion mirror is combined with a fixed mirror, so as to reflect the light beam a plurality of times between the fixed mirror and the torsion mirror. As a result it is possible to increase the light beam deflection speed and to increase the deflection angle of the light beam. Such an optical deflecting unit which uses the torsion mirror is proposed in a Japanese Laid-Open Patent Application No.4-52618, for example, and for the sake of convenience, the optical deflection method which uses the multiple reflections of the between the fixed mirror and the torsion mirror will hereinafter be referred to as a xe2x80x9cmultiple reflection deflectionxe2x80x9d method.
Recently, a micro torsion mirror which makes a sinusoidal pivoting and is capable of making a high-speed deflection has been developed in the field of micromachines. Accordingly, the optical scan speed can be increased by use of such a micro torsion mirror.
However, when the proposed multiple reflection deflection method described above is employed to deflect the light beam, a skew which will be described later is generated in the deflected light beam, to thereby deteriorate the wavefront aberration of the deflected light beam. When the wavefront aberration of the deflected light beam deteriorates, it becomes impossible to satisfactorily form a beam spot having a small diameter on the scanning surface, and a high-density and high-precision optical scan cannot be made.
Accordingly, it is a general object of the present invention to provide a novel and useful optical deflecting unit, optical scanning unit, image forming apparatus and method of producing optical unit, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide an optical deflecting unit, optical scanning unit, image forming apparatus and method of producing optical unit, which can realize the multiple reflection deflection with a high light beam deflection speed and a large deflection angle of the light beam, and with an effectively reduced skew of the deflected light beam.
Still another object of the present invention is to provide an optical deflecting unit for deflecting a light beam in a main scan direction, comprising a torsion mirror which is pivotable about an axis and having a deflecting reflection surface which receives the light beam at an incident angle inclined with respect to a plane which is perpendicular to the axis and the deflecting reflection surface; and at least one fixed mirror surface confronting the torsion mirror and arranged so that the light beam is reflected between the torsion mirror and the at least one fixed mirror surface a plurality of times, and a moving direction of a reflection position of the light beam on the torsion mirror in a sub scan direction reverses, the sub scan direction being perpendicular to the main scan direction. According to the optical deflecting unit of the present invention, it is possible to realize the multiple reflection deflection with a high light beam deflection speed and a large deflection angle of the light beam, and with an effectively reduced skew of the deflected light beam.
A further object of the present invention is to provide an optical deflecting unit for deflecting a light beam in a main scan direction, comprising a first substrate pivotally supporting a torsion mirror having a deflecting reflection surface; a second substrate disposed to confront the first substrate, the second substrate having a bonding surface parallel to the first substrate and at least one fixed mirror surface which is inclined in a sub scan direction with respect to the deflecting reflection surface, the sub scan direction being perpendicular to the main scan direction, where the light beam first reaches the deflecting reflection surface and is reflected a plurality of times between the deflecting reflection surface and the at least one fixed mirror surface before being output as a deflected light beam. According to the optical deflecting unit of the present invention, it is possible to realize the multiple reflection deflection with a high light beam deflection speed and a large deflection angle of the light beam, and with an effectively reduced skew of the deflected light beam.
Another object of the present invention is to provide an optical scanning unit for scanning a body by a light beam in a main scan direction, comprising an optical deflecting unit which deflects a light beam in the main scan direction; and a lens system for imaging a deflected light beam from the optical deflecting unit on the body, where the optical deflecting unit comprises a torsion mirror which is pivotable about an axis and having a deflecting reflection surface which receives the light beam at an incident angle inclined with respect to a plane which is perpendicular to the axis and the deflecting reflection surface; and at least one fixed mirror surface confronting the torsion mirror and arranged so that the light beam is reflected between the torsion mirror and the at least one fixed mirror surface a plurality of times, and a moving direction of a reflection position of the light beam on the torsion mirror in a sub scan direction reverses so as to reduce a skew of the deflected light beam, the sub scan direction being perpendicular to the main scan direction. According to the optical scanning unit of the present invention, it is possible to realize the multiple reflection deflection with a high light beam deflection speed and a large deflection angle of the light beam, and with an effectively reduced skew of the deflected light beam.
Still another object of the present invention is to provide an optical scanning unit for scanning a body by a light beam in a main scan direction, comprising an optical deflecting unit which deflects a light beam in the main scan direction; and a lens system for imaging a deflected light beam from the optical deflecting unit on the body, where the optical deflecting unit comprises a first substrate pivotally supporting a torsion mirror having a deflecting reflection surface; a second substrate disposed to confront the first substrate, the second substrate having a bonding surface parallel to the first substrate and at least one fixed mirror surface which is inclined in a sub scan direction with respect to the deflecting reflection surface so as to reduce a skew of the deflected light beam, the sub scan direction being perpendicular to the main scan direction, where the light beam first reaches the deflecting reflection surface and is reflected a plurality of times between the deflecting reflection surface and the at least one fixed mirror surface before being output as the deflected light beam. According to the optical scanning unit of the present invention, it is possible to realize the multiple reflection deflection with a high light beam deflection speed and a large deflection angle of the light beam, and with an effectively reduced skew of the deflected light beam.
A further object of the present invention is to provide an image forming apparatus comprising a photoconductive body; an optical scanning unit which outputs a light beam which is deflected in a main scan direction; and a lens system for imaging the deflected light beam from the optical deflecting unit on the photoconductive body, where the optical scanning unit comprises a torsion mirror which is pivotable about an axis and having a deflecting reflection surface which receives the light beam at an incident angle inclined with respect to a plane which is perpendicular to the axis and the deflecting reflection surface; and at least one fixed mirror surface confronting the torsion mirror and arranged so that the light beam is reflected between the torsion mirror and the at least one fixed mirror surface a plurality of times, and a moving direction of a reflection position of the light beam on the torsion mirror in a sub scan direction reverses so as to reduce a skew of the deflected light beam, the sub scan direction being perpendicular to the main scan direction. According to the image forming apparatus of the present invention, it is possible to realize the multiple reflection deflection with a high light beam deflection speed and a large deflection angle of the light beam, and with an effectively reduced skew of the deflected light beam.
Another object of the present invention is to provide an image forming apparatus comprising a photoconductive body; an optical scanning unit which outputs a light beam which is deflected in a main scan direction; and a lens system for imaging the deflected light beam from the optical deflecting unit on the photoconductive body, where the optical scanning unit comprises a first substrate pivotally supporting a torsion mirror having a deflecting reflection surface; a second substrate disposed to confront the first substrate, the second substrate having a bonding surface parallel to the first substrate and at least one fixed mirror surface which is inclined in a sub scan direction with respect to the deflecting reflection surface so as to reduce a skew of the deflected light beam, the sub scan direction being perpendicular to the main scan direction, the light beam first reaching the deflecting reflection surface and being reflected a plurality of times between the deflecting reflection surface and the at least one fixed mirror surface before being output as the deflected light beam. According to the image forming apparatus of the present invention, it is possible to realize the multiple reflection deflection with a high light beam deflection speed and a large deflection angle of the light beam, and with an effectively reduced skew of the deflected light beam.
Still another object of the present invention is to provide a method of producing an optical unit which deflects a light beam in a main scan direction, comprising the steps of (a) preparing a first substrate pivotally supporting a torsion mirror having a deflecting reflection surface; (b) disposing a second substrate on the first substrate via a spacer, the second substrate having a bonding surface parallel to the first substrate and at least one fixed mirror surface which is inclined in a sub scan direction with respect to the deflecting reflection surface so as to reduce a skew of the deflected light beam, the sub scan direction being perpendicular to the main scan direction, the light beam first reaching the deflecting reflection surface and being reflected a plurality of times between the deflecting reflection surface and the at least one fixed mirror surface before being output as the deflected light beam; and (c) bonding the first and second substrates and the spacer by matching alignment holes or marks in each of the first and second substrates and the spacer, the alignment holes or marks being smaller towards the first substrate from the second substrate via the spacer. According to the method of producing the optical unit of the present invention, it is possible to realize the multiple reflection deflection with a high light beam deflection speed and a large deflection angle of the light beam, and with an effectively reduced skew of the deflected light beam.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.